1. Field of the Invention
The present invention relates to apparatus and method for calculating a mass air quantity sucked into a cylinder of an internal combustion engine while performing income and outgo calculations of an air mass in an intake manifold on the basis of an output signal of an airflow meter located at an upstream side of the intake manifold.
2. Description of the Related Art
A cylinder intake-air (or sucked air) quantity is calculated with a relationship of a first-order lag to an intake air quantity measured by the airflow meter through a weighted mean process in order to cope with a stepwise variation in an opening angle of a throttle valve, in a normally available engine which controls the intake air quantity through a control over an engine throttle valve to calculate the cylinder intake air quantity. This is exemplified by a Japanese Patent Application First Publication No. Showa 61-258942 published on Nov. 17, 1986.
However, in a variably operated engine valve equipped internal combustion engine which is capable of controlling arbitrarily open-and-closure timings of intake and exhaust valves, a control over timings at which the intake valve is opened or closed and the exhaust valve is opened or closed, particularly, a control of a closure timing of the intake valve causes the cylinder intake-air quantity to be varied in a stepwise manner. Hence, the above-described method cannot calculate, with a high accuracy, the cylinder intake-air quantity.
A Japanese Patent Application First Publication No. 2001-20787 published on Jan. 23, 2001 (which corresponds to a U.S. Pat. No. 6,328,007 issued on Dec. 11, 2001) exemplifies a previously proposed cylinder sucked mass air quantity calculating apparatus. That is to say, the mass air quantity within the intake manifold is calculated by performing income and outgo calculations of the mass air quantity flowing into the intake manifold calculated from the output of the airflow meter and that flowing out into the cylinder. On the other hand, a volumetric air quantity sucked into the cylinder is calculated on the basis of valve open-and-closure timings of the corresponding intake and exhaust valves. Then, the mass air quantity sucked into the cylinder is calculated from the mass air quantity within the intake manifold, an air density calculated from the volume of the intake manifold previously determined, and the volumetric air quantity sucked into the cylinder. According to the above-described method of calculating the cylinder sucked mass air quantity, the cylinder sucked air quantity can accurately be calculated.
It is preferable to store a calculated value of the mass air quantity within the intake manifold into a memory during a stop of the engine so as to be used for a time during which a restart of the engine is carried out in order to secure sufficiently an accuracy of the above-described cylinder sucked intake-air quantity.
FIG. 12 shows a variation pattern of a total piston stroke variable during a stop of the engine.
As shown in FIG. 12, even after the engine has stopped, the air flows into the intake manifold due to a negative pressure left present in the intake manifold so that the air flows into a portion of connecting the intake manifold to a cylinder volume communicated with the intake manifold until the portion is settled at the atmospheric pressure.
However, since, in the income and outgo calculations of the mass air quantity within the intake manifold, the mass air quantity of the air flowing out from the intake manifold is calculated to give zero after the detection of the engine stop (engine revolution has been stopped), the mass air quantity within the intake manifold calculated during the stop of the engine is resulted in a value of adding in an extra manner the air quantity corresponding to the cylinder volume communicated with the intake manifold.
It is noted that, if a crank angular position during a stop of the engine is placed at a constant position, a volume of the cylinder communicated with the intake manifold is accordingly constant. Therefore, a constant initial value may be given as the mass air quantity within the intake manifold during a re-start of the engine. However, in an actual practice, the crank angular position does not indicate constant due to various types of primary factors.
FIG. 13 shows a total stroke variable (which is approximately proportional to a total cylinder volume) which is a total of stroke variables of respective pistons from its upper top dead center of respective cylinders communicated with the intake manifold with respect to the crank angular position during the stop of the engine. In FIG. 13, a dot-and-dash line denotes the piston stroke variable of each cylinder in which the piston stroke variable is varied in a stepwise manner when the intake valve is started to open so as to be communicated with the intake manifold and when the intake valve is closed to block the communication of the corresponding cylinder with the intake manifold.
FIG. 14 shows a total cylinder volume which is a total of each cylinder communicated with the intake manifold with respect to the crank angular position during the stop of engine 1, in a case of a four-cylinder engine and in a case of a sixth-cylinder engine. The total number volume is approximately proportional to the total stroke variables. As shown in FIG. 14, the total cylinder volume is largely different between maximum cylinder volume and minimum cylinder volume. In general, at a time point at which a plurality of cylinders are communicated with the intake manifold due to a balance of each force, the engine is often stopped (an interval of A shown in FIG. 14). Even in this case, a considerable variation is present. In addition, there is often a case where the engine cylinders are balanced in a state where a connecting rod raised perpendicularly at the upper top dead center receives a compression reaction force (an interval B in FIG. 14).
As described above, if a large variation occurs in the cylinder volume communicated with the intake manifold during the stop of the engine, the initial value of the mass air quantity within the intake manifold during the re-start of the engine cannot accurately be calculated and errors occur in the subsequent income and outgo calculation and the calculation of the cylinder intake-air quantity. A Japanese Patent No. 2901613 issued on Mar. 19, 1999 (which corresponds to a U.S. Pat. No. 4,911,133 issued on Mar. 27, 1990) exemplifies a still another previously proposed cylinder sucked air quantity calculating apparatus in which, when a total weight of the intake-air system located at a downstream side of the throttle valve is calculated, the initial value is calculated with a pressure located downstream of the throttle valve set as the atmospheric pressure. However, in this Japanese Patent, no consideration on which way, specifically, the atmospheric pressure is determined is given and no consideration is given on the cylinder volume communicated with the intake manifold which is different according to the crank angular position.
It is, hence, an object of the present invention to provide cylinder intake-air quantity calculating apparatus for an internal combustion engine which can accurately detect the mass air quantity within the intake manifold during the stop of the engine so that the cylinder sucked air quantity can always accurately be calculated.
According to one aspect of the present invention, there is provided an apparatus for calculating a mass air quantity sucked into one of cylinders of an internal combustion engine, comprising: a cylinder sucked mass air quantity calculating section that calculates a mass air quantity sucked into a corresponding one of the cylinders of the engine on the basis of a mass air quantity within an intake manifold and a volume of the corresponding cylinder while performing income and outgo calculations between a mass air quantity flowing into the intake manifold and that flowing out from the intake manifold to calculate the mass air quantity within the intake manifold; and a correction section that corrects the mass air quantity within the intake manifold calculated as a result of the income and outgo calculations between the mass air quantities during a stop of the engine on the basis of a crank angular position during the stop of the engine to calculate finally the mass air quantity within the intake manifold during the stop of the engine.
According to another aspect of the present invention, there is provided a method for calculating a mass air quantity sucked into one of cylinders of an internal combustion engine, comprising: performing income and outgo calculations between a mass air quantity flowing into an intake manifold and that flowing out from the intake manifold to calculate the mass air quantity within the intake manifold; calculating a mass air quantity sucked into a corresponding cylinder of the engine on the basis of the mass air quantity within the intake manifold and a volume of the corresponding cylinder; and correcting the mass air quantity within the intake manifold calculated as a result of the income and outgo calculations of the mass air quantity during a stop of the engine on the basis of a crank angular position at a time at which the engine has stopped to calculate finally the mass air quantity within the intake manifold during the stop of the engine.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.